System and method for calculating distance to empty of green vehicle

ABSTRACT

Disclosed is a system and method for computing distance to empty (DTE) based on available energy computed using a battery SOC vs open circuit voltage (OCV) table, battery temperature vs energy efficiency, an energy efficiency vs energy table, etc., to enable a more accurate calculation of the DTE in consideration of the temperature of the battery, which is one of disturbance elements.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims under 35 U.S.C. §119(a) the benefit of KoreanPatent Application No. 10-2012-0108488 filed Sep. 28, 2012, the entirecontents of which are incorporated herein by reference.

BACKGROUND

(a) Technical Field

The present invention relates to a system and method for calculatingdistance to empty (DTE) of a green vehicle. More particularly, thepresent invention relates to a system and method for calculating a DTEof a green vehicle, which can compute available energy of a battery andmore accurately compute DTE using the computed available energy.

(b) Background Art

Green vehicles are considered as any green vehicle which does notdischarge exhaust gas. These types of vehicles include a pure electricvehicle driven using power of an electric motor, a hybrid vehicledriving using combined power from a motor and an engine, a fuel cellvehicle driven via power from an electric motor operated by electricitygenerated within a fuel cell, or any other vehicle that hassubstantially lower emissions that a conventional internal combustionvehicle.

A high-voltage battery as an electric power source for driving a motor,a converter, etc., are often mounted in such a green vehicle. Thecurrent status of the battery should be maintained at a satisfactorylevel by monitoring the voltage, current, temperature, etc. of thebattery and estimating a temperature of the battery and a degree ofdegradation of the battery including a state of charge (SOC) [%] of thebattery. Therefore, a battery management system (BMS), e.g., a kind ofcontroller, is mounted in the green vehicle, to generally manage variousstates of the battery, preventing reduction in lifespan of the batterydue to the degradation of durability of the battery, estimating the SOCof the battery, and the like.

As such, it is very important to detect the SOC of the battery in thegreen vehicle using the high-voltage battery. Particularly, it isrequired to develop a technique for informing a driver of distance toempty (DTE) through the medium of a cluster by detecting the SOC of thebattery, etc., while driving.

Generally, in gasoline and diesel vehicles, a system and method isapplied in which a current DTE is predicted in such a manner thatmeasures the amount of fuel in a fuel tank using a sensor, etc. andmultiplies accumulated fuel efficiency by the amount of remaining fuel.However, in green vehicles, the current DTE is predicted by measuringthe amount of discharge current used per unit of time (e.g., a second orminute) in a battery and accordingly estimates a current SOC of thebattery.

Hereinafter, a conventional method for DTE computation of a greenvehicle will be described with reference FIGS. 1 and 2. First, a currentSOC of a battery is estimated by an SOC computation unit 10 within acontroller.

Estimating the current SOC of the battery is performed by measuring theamount of discharging current used per unit of time in the battery andaccumulating the measured amounts and then correcting the SOC byadding/subtracting data on disturbance elements (e.g., temperature anddegradation of the battery) data and an open circuit voltage (OCV) forvoltage compensation of the battery to/from current accumulated data.

Next, a current DTE is computed based on an SOC estimated in a DTEcomputation unit 40. In this case, the estimated SOC and the computedDTE are stored in a memory 60. Thus, the current DTE is finally computedin such a manner that adds/subtracts an initial value of DTE accordingto a learning logic to/from the DTE computed based on the estimated SOC.Then, the finally computed current DTE is displayed in a cluster display50 so that a driver can identify the current DTE.

When a driver starts the vehicle in an indoor parking state and drivesthe vehicle outdoors or parks the vehicle outdoors, external temperatureis lowered. However, as the temperature of the battery among disturbanceelements is not considered in the computation of the DTE, thetemperature of the battery is also lowered. Therefore, the DTE is notaccurately computed but computed rather excessively (i.e., high).Further, the DTE is rapidly reduced in a low SOC of the battery duringlong-distance driving.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY OF THE DISCLOSURE

The present invention has been made in an effort to solve theabove-described problems associated with prior art. Accordingly, thepresent invention provides a system and method for distance to empty(DTE) computation of a green vehicle, which does not employ aconventional system and method for computing DTE based on the state ofcharge (SOC) of a battery but rather employs a method for computing DTEbased on available energy computed using a battery SOC vs open circuitvoltage (OCV) table, battery temperature vs energy efficiency, an energyefficiency vs energy table, etc., to enable a more accurate calculationof the DTE in consideration of the temperature of the battery, which isone of a plurality of disturbance elements effecting the efficiency of abattery.

In one aspect, the present invention provides a method for DTEcomputation of a green vehicle, the method including: computing, by acontroller, a current available energy of a battery, based on energyefficiency (η) of the battery, available energy when the state of charge(SOC) is 100% (E_(@SOC=100%)) extracted from an energy efficiency vsenergy table, and information on real-time SOC (%); computing, by thecontroller, DTE based on the computed available energy; and displaying,on the display, the computed DTE in a cluster.

In an exemplary embodiment, the energy efficiency (η) may be computed byestimating, by the controller, an SOC in a load state in which thebattery is discharged; extracting, by the controller, an open circuitvoltage and a current corresponding to the current SOC estimated from abattery SOC vs open circuit voltage (OCV) table; and computing, by thecontroller, an energy efficiency of the battery by substituting theextracted open circuit voltage and the current in:

${{Energy}\mspace{14mu} {efficiency}\mspace{14mu} (\eta)} = {\left( {1 - \frac{\int{{{i \cdot \left( {v_{t} - v_{e}} \right)}}{t}}}{{\int{{{i \cdot v_{i}}}{t}}} + {\int{{{i \cdot v_{e}}}{t}}}}} \right) \cdot 100.}$

In another exemplary embodiment, when estimating the SOC, the estimatedcurrent SOC may be stored in an SOC memory of the controller so as to beused in the computation of the available energy.

In still another exemplary embodiment, the energy efficiency (η) may becomputed by measuring a temperature of a battery in a non-load state inwhich the battery is discharged; and extracting energy efficiencycorresponding to the measured temperature of the battery by substitutingthe measured temperature of the battery in a battery temperature vsenergy efficiency table.

In yet another exemplary embodiment, the available energy may becomputed by substituting, by the controller, the energy efficiency ofthe battery in the energy efficiency vs energy table, thereby extractingthe available energy when the state of charge (SOC) is 100%(E_(@SOC=100%)); and the energy efficiency (η) of the battery, theavailable energy when the state of charge (SOC) is 100% (E_(@SOC=100%)),extracted from the SOC memory, and the information on real-time SOC (%)in:

${{Energy}\mspace{14mu} {efficiency}\mspace{14mu} (\eta)} = {\left( {1 - \frac{\int{{{i \cdot \left( {v_{t} - v_{e}} \right)}}{t}}}{{\int{{{i \cdot v_{i}}}{t}}} + {\int{{{i \cdot v_{e}}}{t}}}}} \right) \cdot 100.}$

In still yet another exemplary embodiment, the DTE may be computed by amultiplication of battery-electric efficiency (km/kwh) and availableenergy.

Other aspects and exemplary embodiments of the invention are discussedinfra.

As described above, the present invention employs a method for computingavailable energy supplied from the battery using the battery SOC vs OCVtable, the battery temperature vs energy efficiency, the energyefficiency vs energy table, etc., and computing DTE based on theavailable energy, so that the DTE can be more accurately computed anddisplayed even during the winter, etc., in consideration of thetemperature of the battery, which is one of a plurality of disturbanceelements that effects a battery's efficiency.

Thus, it is possible to solve a problem in that DTE is not accuratelycomputed since the DTE is computed based on only the battery SOC withoutconsidering the temperature of the battery among the disturbanceelements. Particularly, as the temperature of the battery is changed dueto a difference in temperature between interior and exterior of avehicle during winter.

The above and other features of the invention are discussed infra.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present invention will now bedescribed in detail with reference to certain exemplary embodimentsthereof illustrated the accompanying drawings which are givenhereinbelow by way of illustration only, and thus are not limitative ofthe present invention, and wherein:

FIGS. 1 and 2 are respectively a control diagram and a flowchartillustrating a conventional method for driving to empty (DTE)computation of a green vehicle;

FIGS. 3 and 4 are respectively a control diagram and a flowchartillustrating a method for driving to DTE computation of a green vehicleaccording to an exemplary embodiment of the present invention;

FIGS. 5 and 6 are graphs illustrating the definition and computingprocess of available energy used when the DTE of the green vehicle iscomputed according to the exemplary embodiment of the present invention;

FIG. 7 is a detailed control diagram illustrating in detail the methodfor the DTE computation of the green vehicle according to an exemplaryembodiment of the present invention; and

FIG. 8 is a diagram illustrating an energy efficiency vs temperaturetable used when the DTE of the green vehicle is computed according tothe exemplary embodiment of the present invention.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variouspreferred features illustrative of the basic principles of theinvention. The specific design features of the present invention asdisclosed herein, including, for example, specific dimensions,orientations, locations, and shapes will be determined in part by theparticular intended application and use environment.

In the figures, reference numbers refer to the same or equivalent partsof the present invention throughout the several figures of the drawing.

DETAILED DESCRIPTION

Hereinafter reference will now be made in detail to various embodimentsof the present invention, examples of which are illustrated in theaccompanying drawings and described below. While the invention will bedescribed in conjunction with exemplary embodiments, it will beunderstood that present description is not intended to limit theinvention to those exemplary embodiments. On the contrary, the inventionis intended to cover not only the exemplary embodiments, but alsovarious alternatives, modifications, equivalents and other embodiments,which may be included within the spirit and scope of the invention asdefined by the appended claims.

It is understood that the term “vehicle” or “vehicular” or other similarterm as used herein is inclusive of motor vehicles in general such aspassenger automobiles including sports utility vehicles (SUV), buses,trucks, various commercial vehicles, watercraft including a variety ofboats and ships, aircraft, and the like, and includes hybrid vehicles,electric vehicles, plug-in hybrid electric vehicles, hydrogen-poweredvehicles and other alternative fuel vehicles (e.g., fuels derived fromresources other than petroleum). As referred to herein, a hybrid vehicleis a vehicle that has two or more sources of power, for example bothgasoline-powered and electric-powered vehicles.

Additionally, it is understood that the below methods are executed by atleast one controller. The term controller refers to a hardware devicethat includes a memory and a processor. The memory is configured tostore the modules and the processor is specifically configured toexecute said modules to perform one or more processes which aredescribed further below.

Furthermore, the control logic of the present invention may be embodiedas non-transitory computer readable media on a computer readable mediumcontaining executable program instructions executed by a processor,controller or the like. Examples of the computer readable mediumsinclude, but are not limited to, ROM, RAM, compact disc (CD)-ROMs,magnetic tapes, floppy disks, flash drives, smart cards and optical datastorage devices. The computer readable recording medium can also bedistributed in network coupled computer systems so that the computerreadable media is stored and executed in a distributed fashion, e.g., bya telematics server or a Controller Area Network (CAN).

The present invention employs a system and method for computing distanceto empty (DTE) based on available energy of a battery to enable a moreaccurate computation of the DTE in consideration of a temperature of thebattery, which is one of disturbance elements affecting the efficiencyof a battery.

First, for better understanding of the present invention, availableenergy of a battery will be described.

The available energy is expressed as a function using temperature,degradation, state of charge (SOC), etc. of the battery as variablefactors. As shown in FIG. 5, it can be seen that the available energysupplied from the battery is changed depending on the temperature of thebattery. It can also be seen that the energy efficiency of the batteryincreases as the temperature of the battery rises, and thus theavailable energy increases. In this case, the energy efficiency isexpressed as shown in the following Equation 1.

$\begin{matrix}{{\therefore{{Energy}\mspace{14mu} {efficiency}\mspace{14mu} (\eta)}} = {\left( {1 - \frac{\int{{{i \cdot \left( {v_{t} - v_{e}} \right)}}{t}}}{{\int{{{i \cdot v_{i}}}{t}}} + {\int{{{i \cdot v_{e}}}{t}}}}} \right) \cdot 100}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

In the above Equation 1, i denotes current, V_(t) denotes a terminalvoltage of the battery, V_(e) denotes an open circuit voltage of thebattery, ∫|i·v_(t)|dt and ∫|i·v_(e)|dt denote charging and dischargingenergy (hereinafter, referred to as charging/discharging energy), and∫|i·(v_(t)−v_(e))|dt denotes heat loss energy generated when the batteryis charged and discharged.

Hereinafter, a series of processes of computing available energy basedon the energy efficiency of the battery and then computing DTE in loadand non-load states of the battery will be sequentially described withreference to FIGS. 3 to 8.

Load State of Battery

When the battery is in a load state in which the battery is dischargedafter the ignition of the vehicle is on, a current SOC of the battery isestimated by an SOC computation unit 10 executed by a processor in acontroller. Estimating the current SOC is performed by measuring, by thecontroller, amounts of discharging current used per unit of time (e.g.,seconds, minutes, hours, etc.) in the battery and accumulating themeasured amounts and correcting the SOC by adding/subtracting an opencircuit voltage (OCV) for voltage compensation of the battery.

Next, the estimated current SOC is substituted in a map table of an OCVcomputation unit 20, i.e., a battery SOC vs OCV table data-mappedthrough tests, thereby obtaining an OCV corresponding to the estimatedcurrent SOC from the battery SOC vs OCV table. In this case, theestimated current SOC is an SOC memory unit 60 so as to be obtained whenavailable energy is computed.

Next, the available energy of the battery is computed in an availableenergy computation unit 30 via, e.g., a processor in the controller.Therefore, computing energy efficiency of the battery is performed as apreceding step. That is, once an open circuit voltage and currentcorresponding to the current SOC is obtained from the battery SOC vs OCVtable and then input to the available energy computation unit 30, theenergy efficiency of the battery is computed by Equation 1.

Subsequently, energy of the battery when the SOC is 100% (E_(@SOC=100%))is determined by substituting the energy efficiency of the battery,computed as described above, in an energy efficiency vs energy tabledata-mapped through tests, and the available energy is then computed.

FIG. 6 illustrates available energy for each temperature and SOC of thebattery at 1C-rate (capacity of the battery, which can be used for 1hour). As can be seen in FIG. 6, the energy efficiency and availableenergy are changed depending on the temperature of the battery. Forexample, as can be seen in (b) of FIG. 6, available energy as comparedwith energy efficiency when the temperature of the battery is 25° C. isdifferent from that when the temperature of the battery is −30° C. Ascan be seen in (a) of FIG. 6, energy efficiency and available energywhen the SOC is 100% corresponding to the energy efficiency can beobtained for each temperature (25° C., 10° C., −10° C. and −30° C.), andthus the energy efficiency vs energy table can be data-mapped in thesame manner as the graph shown in (c) of FIG. 6. Thus, when the energyefficiency of the battery, computed by Equation 1, is substituted in theenergy efficiency vs energy table, the available energy when the SOC is100% (E_(@SOC=100%)) can be obtained.

Subsequently, the current available energy of the battery can becomputed using the following Equation 2, based on the energy efficiency(η) computed by Equation 1, the available energy when the SOC is 100%(E_(@SOC=100%)) extracted from the energy efficiency vs energy table,and information on real-time SOC (%) extracted from the SOC memory unit.

$\begin{matrix}{{{Available}\mspace{14mu} {energy}} = {\frac{E_{{@{SOC}} = {100\%}}}{\eta}\left\{ {{SOC} - \left( {100 - \eta} \right)} \right\}}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

Next, DTE is computed based on the available energy of the battery,computed as described above, by a DTE computation unit 40. The DTE isobtained by a multiplication of battery-electric efficiency (km/kwh) andavailable energy, and the battery-electric efficiency is computed by thefollowing Equation 3.

Battery-electric efficiency(km/kwh)=battery-electricefficiency(past)*A+battery-electric efficiency(present)*B+partialelectric efficiency(present)*C  Equation 3

In Equation 3, A, B and C denote adjustable weights (coefficients).

Finally, DTE obtained by the multiplication of battery-electricefficiency (km/kwh) and available energy is displayed in a clusterdisplay 50 so that a driver can identify the DTE. Meanwhile, the factorsused in the computation, i.e., the real-time SOC, the available energy,etc., including the DTE computed as described above, are stored in amemory or other storage device and then used as initial values in anon-load state after the ignition of the vehicle is on (IG ON).

Non-Load State of Battery

When the battery is in a non-load state in which the battery is notdischarged after the ignition of the vehicle is on, the SOC estimated inthe load state and then stored in the SOC memory or other storage deviceis used as an SOC initial value. Next, energy efficiency of the batteryis computed by the controller according to the temperature of thebattery.

As shown in FIG. 7, data in a map table for battery temperature vsenergy efficiency can be obtained through tests, when considering thatthe energy efficiency exponentially decreases as the temperature of thebattery decreases, and the energy efficiency exponentially increases asthe temperature of the battery increases. Accordingly, when thetemperature of the battery, measured using a temperature sensor, etc.,is substituted in a battery temperature vs energy efficiency table, theenergy efficiency corresponding to the measured temperature of thebattery is extracted.

Next, like the load state of the battery, the available energy when theSOC is 100% (E_(@SOC=100%)) is extracted by substituting the extractedenergy efficiency of the battery in the energy efficiency vs energytable data-mapped through tests in the available energy computation unit30, and the available energy is then computed. Subsequently, the currentavailable energy of the battery can be computed using the Equation 2,based on the energy efficiency (η) extracted from the batterytemperature vs energy efficiency table, the available energy when theSOC is 100% (E_(@SOC=100%)) extracted from the energy efficiency vsenergy table, and information on real-time SOC (%) extracted from theSOC memory or other storage device in the load state.

Next, DTE is computed based on the available energy of the battery,computed in the DTE computation unit 40 as described above in the samemanner as the load state of the battery, and therefore, its detaileddescription will be omitted. Finally, DTE obtained by the multiplicationof battery-electric efficiency (km/kwh) and available energy isdisplayed in a cluster display 50 so that a driver can identify the DTE.

As described above, the present invention employs a system and method ofcomputing available energy supplied from the battery and computing DTEbased on the available energy, so that the DTE can be more accuratelycomputed and displayed even in winter season, etc., in consideration ofthe temperature of the battery, which is one of disturbance elementsaffecting battery efficiency.

The invention has been described in detail with reference to exemplaryembodiments thereof. However, it will be appreciated by those skilled inthe art that changes may be made in these embodiments without departingfrom the principles and spirit of the invention, the scope of which isdefined in the appended claims and their equivalents.

What is claimed is:
 1. A method for distance to empty (DTE) computationof a green vehicle, the method comprising: computing, by a controller, acurrent available energy of a battery, based on energy efficiency (η) ofthe battery, available energy when the state of charge (SOC) is 100%(E_(@SOC=100%)) extracted from an energy efficiency vs energy table, andinformation on real-time SOC (%); computing, by the controller, DTEbased on the computed available energy; and displaying, on a display,the computed DTE in a cluster.
 2. The method of claim 1, wherein theenergy efficiency (η) is computed by estimating an SOC in a load statein which the battery is discharged; extracting open circuit voltage andcurrent corresponding to the current SOC estimated from a battery SOC vsopen circuit voltage (OCV) table; and computing energy efficiency of thebattery by substituting the extracted open circuit voltage and currentin:${{Energy}\mspace{14mu} {efficiency}\mspace{14mu} (\eta)} = {\left( {1 - \frac{\int{{{i \cdot \left( {v_{t} - v_{e}} \right)}}{t}}}{{\int{{{i \cdot v_{i}}}{t}}} + {\int{{{i \cdot v_{e}}}{t}}}}} \right) \cdot 100.}$3. The method of claim 2, wherein, in the estimating of the SOC, theestimated current SOC is stored in an SOC memory so as to be used in thecomputation of the available energy.
 4. The method of claim 1, whereinthe energy efficiency (η) is computed by measuring a temperature of abattery in a non-load state in which the battery is discharged; andextracting energy efficiency corresponding to the measured temperatureof the battery by substituting the measured temperature of the batteryin a battery temperature vs energy efficiency table.
 5. The method ofclaim 1, wherein the available energy is computed by substituting theenergy efficiency of the battery in the energy efficiency vs energytable, thereby extracting the available energy when the state of charge(SOC) is 100% (E_(@SOC=100%)); and the energy efficiency (η) of thebattery, the available energy when the state of charge (SOC) is 100%(E_(@SOC=100%)), extracted from the SOC memory, and the information onreal-time SOC (%) in:${{Energy}\mspace{14mu} {efficiency}\mspace{14mu} (\eta)} = {\left( {1 - \frac{\int{{{i \cdot \left( {v_{t} - v_{e}} \right)}}{t}}}{{\int{{{i \cdot v_{i}}}{t}}} + {\int{{{i \cdot v_{e}}}{t}}}}} \right) \cdot 100.}$6. The method of claim 1, wherein the DTE is computed by amultiplication of battery-electric efficiency (km/kwh) and availableenergy.
 7. A non-transitory computer readable medium containing programinstructions executed by a processor or controller, the computerreadable medium comprising: program instructions that compute a currentavailable energy of a battery, based on energy efficiency (η) of thebattery, available energy when the state of charge (SOC) is 100%(E_(@SOC=100%)) extracted from an energy efficiency vs energy table, andinformation on real-time SOC (%); program instructions that compute DTEbased on the computed available energy; and program instructions thatdisplay the computed DTE in a cluster.
 8. The non-transitory computerreadable medium of claim 7, wherein the energy efficiency (η) iscomputed by estimating an SOC in a load state in which the battery isdischarged; extracting open circuit voltage and current corresponding tothe current SOC estimated from a battery SOC vs open circuit voltage(OCV) table; and computing energy efficiency of the battery bysubstituting the extracted open circuit voltage and current in:${{Energy}\mspace{14mu} {efficiency}\mspace{14mu} (\eta)} = {\left( {1 - \frac{\int{{{i \cdot \left( {v_{t} - v_{e}} \right)}}{t}}}{{\int{{{i \cdot v_{i}}}{t}}} + {\int{{{i \cdot v_{e}}}{t}}}}} \right) \cdot 100.}$9. The non-transitory computer readable medium of claim 8, wherein, inthe estimating of the SOC, the estimated current SOC is stored in an SOCmemory so as to be used in the computation of the available energy. 10.The non-transitory computer readable medium of claim 7, wherein theenergy efficiency (η) is computed by measuring a temperature of abattery in a non-load state in which the battery is discharged; andextracting energy efficiency corresponding to the measured temperatureof the battery by substituting the measured temperature of the batteryin a battery temperature vs energy efficiency table.
 11. Thenon-transitory computer readable medium of claim 7, wherein theavailable energy is computed by substituting the energy efficiency ofthe battery in the energy efficiency vs energy table, thereby extractingthe available energy when the state of charge (SOC) is 100%(E_(@SOC=100%)); and the energy efficiency (η) of the battery, theavailable energy when the state of charge (SOC) is 100% (E_(@SOC=100%)),extracted from the SOC memory, and the information on real-time SOC (%)in:${{Energy}\mspace{14mu} {efficiency}\mspace{14mu} (\eta)} = {\left( {1 - \frac{\int{{{i \cdot \left( {v_{t} - v_{e}} \right)}}{t}}}{{\int{{{i \cdot v_{i}}}{t}}} + {\int{{{i \cdot v_{e}}}{t}}}}} \right) \cdot 100.}$12. The non-transitory computer readable medium of claim 7, wherein theDTE is computed by a multiplication of battery-electric efficiency(km/kwh) and available energy.